handle unknown args passed to Trainer.from_argparse_args

[awaelchli]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?
• If you made a notable change (that affects users), did you update the CHANGELOG?

What does this PR do?

Fixes #1929

Trainer **kwargs was recently removed #1820

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

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[codecov]

Codecov Report

Merging #1932 into master will increase coverage by 0%.
The diff coverage is 80%.

@@          Coverage Diff           @@
##           master   #1932   +/-   ##
======================================
  Coverage      88%     88%           
======================================
  Files          74      74           
  Lines        4621    4623    +2     
======================================
+ Hits         4050    4052    +2     
  Misses        571     571           

[mergify]

This pull request is now in conflict... :(

[williamFalcon]

yup ran into this myself lol...

[awaelchli]

thanks for the merge, great!